Method and apparatus for transmitting intelligence



April 2, 1963 W. J. GREENE METHOD AND APPARATUS FOR TRANSMITTING INTELLIGENCE Filed Sept. 16, 1958 7 Sheets-Sheet 1 RECORDER slNx CHANNEL B-- CO X 20 s I "a 7 CHANNEL r REFERENCE CHANNEL r44 56 4h P DATUM 11:: REFERENCE CHANNEL r48 40 41 29d. 29 1/ 28 SIN Y 29a. 2111i 9b J CHANNEL L M 27 .l FIG. I

II 7 3 V I INVENTOR. cos Y WILLIAM J.GREENE CHANNEL 326x j 32b 49 I Hliwwmh +25ov 51 50 s2 ATTORNEY 8 AGENT W. J. GREENE April 2, 1963 METHOD AND APPARATUS FOR TRANSMITTING INTELLIGENCE Filed Sept. 16, 1958 7 Sheets-Sheet 2 ATTORNEY 6 AGENT April 2, 1963 w. J. GREENE 3,084,333

METHOD AND APPARATUS FOR TRANSMITTING INTELLIGENCE Filed Sept. 16, 1958 7 SheetsSheet 3 v a a a N i-Mw-vwm-NWH (I) d I; l 2 l 4 JZ u I 2 (I A U A (I w "I 1 in (0 J r 8 g 8 d g n w Id .1 I: i D lalz & I!) (I I Q l- U 3 g INVENTOR. I WILLIAM J. GREENE ATTORNEY & AGE NT April 2, 1963 w. J. GREENE METHOD AND APPARATUS FOR TRANSMITTING INTELLIGENCE Filed Sept. 16, 1958 '7 Sheets-Sheet 4.

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W. J. GREENE April 2, 1963 METHOD AND APPARATUS FOR TRANSMITTING INTELLIGENCE Filed Sept. 16, 1958 7 Sheets-Sheet 6 E N 3653mm. 4 Z 0% 7 33.162 kzfibzou M 1 EG M M m a M H Y B mdzz zuu $50 4 2 m0 h 532$ oi H .SE o o! 21 finzxw IPoo m $22 Qz mm n=2 5 5E $225 6 L muzwmmbm 386 m 0 u ATTORNEY 8. AGENT W. J. GREENE April 2, 1963 METHOD AND APPARATUS FOR TRANSMITTING INTELLIGENCE 7 Sheets-Sheet 7 Filed Sept. 16, 1958 Unite States Patent Office 3,084,333 METHOD AND APPARATUS F0192. TRANSMITTING.

llNTELLlGENCE William J; Greene, Scotch Plains, N.J., assignorf to All" Reduction Company, lncorporatedgNew York,1N .Y., a corporation of'NeWYork Filed Sept; 16, W58, Ser- No. 761,423 13 'Ciaims; (Cl. 340--172'.5)

This invention relates to an improved method. and apparatus for transmitting intelligence electrically.

The invention is described herein as applied to a sys tem wherein the intelligence, in the form of an amplitude modulated electrical signal, is coded'and the trzmsmissionis accomplished by recording the intelligence on a magnetic record medium and then playing it back, i.e., reconverting it to an electrical signal. In its broader as pects, the invention is not limited to this particular type of transmission, but has more general utility.

The invention is described herein as applied to a transmission of intelligence toperform a control'function, specifically, to a system for recording a pattern or curve to be followed by a cutting or other forming device. The intelligence represented by the pattern contourmay' be converted to an electrical signal by a tracer control means of the type described in my copending application filed concurrently herewith, Serial No. 761,389, now Patent No. 3,004,166 and entitledv Line Tracer Apparatus and Method. Although my invention has particular utility in connection with the recording of that type of intelli-. gence, and certain features of the invention are particu-. larly intended. for use With such'recording, nevertheless, the broader features of my invention are-- applicable to. any type of intelligencewhich may be represented by an. electrical signal, howeverderived;

in conventional electrical systems for the transmission of intelligence, a carrier, which may be an electrical potential oran-electromagnetic field,- is modulated with time in a transmitter. The modulated carrierthenpasses through a transmission link, which may be alonga wire; through the atmosphere, or along a wave guide. 'The carrier is then demodulated and converted by-'areceiver: to an audible or other sensible signal.

The transmission link between the transmitter and: receivertypically attenuates the signal passing'through' it. The. greater the attenuation, the less intelligible-the signalv from the receiver becomes. The attenuation limitsthe length and other features of'utility of the transmission link. Furthermorawhere the modulation'is by variation in the. amplitude of the carrier, the-modulation may be simulated by stray fields, etc. so as'to introduce noise into thesignal produced by the receiver.

One type of transmission link, as the termis used in this specification, is the recording of an electrical signal; on a magnetic record medium and'a later'reproduction of the recorded signal as an. electricahpotential. Such transmission links are subject to attenuationof the. recorded'signals, just as other transmission links are sub: ject to attenuation. Where the magnetic record'is to be reproduced for control purposes, it is essential that the recordbe reproduced accurately. Attenuation in the recording and reproduction parts of such .a circuit have heretofore limited the. application of such systems to control problems.

In order to avoid attenuation'or' to minimize' itas much as possible, other types of'modulat-ion have been proposed, for example, frequencymodulationand pulse code modulation. These other types of modulation'each have their particular limitations, which are well known in the art. For one reason oranother, these other types of: modulation have notbeen successfully applied commercially to control problems;

An object ofthe present invention is to. provide an improved method and apparatus for the electrical transmission of intelligence.

Another object isto provicle an improvedmethod and apparatus for recordinganelectrical signal on a magnetic record and reproducing that-signal from the magnetic,

record.

Another object is to provide improved method and. apparatus for recording, and reproducing electrical signals with sufficient accuracy so that they may be used as control signals.

Another object is to provide animproved method and apparatus for recording and-reproducing electrical signals fora tracer control system.

Another object ofthe present invention is to provide apparatus for producing an electrical pulse signal Whose.

time spacing from a datum pulse signal is a measure of a voltage amplitude;

Another object of the. invention is to provide an im-- This system of modulation is of particular value Where ahighly accurate reproduction of the transmitted intelligence is required-5 According to the pulse-timecode modulation system, the intelligence .to be transmittedis first converted to an amplitude modulated potential.

The amplitude modulated potential is sampled at fixed intervals of a predetermined frequency substantially higher than the highest frequency of the amplitude mod-. ulated potential. Inthe preferred form of the invention, as described in. detailherein, the intelligence is transmitted over at least three channels or tracks, hereinafter identified, respectively as the cycle reference channel, the

datumrreference channel, and the information channel;

A plurality ofinformation channels may be provided in the same system with' asingle set of cycle and datum reference channels. In the cycle reference channel, pulses. of fixed amplitude are transmitted at the sampling fre-' quency. In the datum reference channel, pulses of fixed amplitude are also transmitted at the sampling frequency. The datum reference pulses occur, however, at different timesl from the cycle reference pulses, being typically half-way between the cycle reference pulses. Thetime of the datum pulse in each cycle represents a datum value of the sampled amplitude modulated potential. Typically, this datum'value may be zero, or ground potential. In the information channel, a pulse occurs during each sampling cycle. The timing of this pulse with respect to the datum pulse is a measure of the amplitude modulated potential at the sampling interval.

A linear relation (i.e., not a quantized relation) is established between'the amplitude modulated potential and the time of the information pulse, so that thereis no quantizingerror in the recording of the inforrnation.

The function of the datum reference pulse and the cycle reference pulse may be combined insome systems utiliz; ing the present invention, as explained in detail below,

Patented Apr. 2, 1963 but a substantial advantage of accuracy is gained by utilizing separate series of pulses for the cycle reference, the datum reference and the information and by utilizing separate channels for the three series of pulses.

' The reproduction of the recorded intelligence is carried out by utilizing the cycle reference pulse to trigger a sawtooth wave generator which produces a saw-tooth wave having substantially equal amplitude swings above and below a predetermined datum. The datum reference pulse samples the saw-tooth wave at its median point. The sampled value is stored, thereby establishing a fixed value for the datum potential. The information reference pulse samples the saw-tooth wave at various times depending on the timing or" the information pulses. The sampled values of potential resulting are stored between samplings and are added algebraically to the datum potential, thereby producing an output potential which accurately reflects the signal originally recorded.

Other objects and advantages of the invention will become apparent from a consideration of the following specifications and claims taken together with the accompanying drawings.

In the drawings:

FIG. 1 is a wiring diagram of a complete recorder constructed in accordance with the invention for use in connection with a tracer control system, and including cycle reference and datum reference channels and four information channels;

FIG. 2 is a more detailed wiring diagram of the cycle reference and datum reference channels of the recorder of FIG. 1; 7

PEG. 3 is a Wiring diagram of a single information channel of the recorder of FIG. 1;

FIG. 4 is a graphical illustration of the variation of certain potentials in the circuit of FIG. 3;

FIGS is a somewhat schematic diagram of a reproducing system which may be used with a record produced by the recorder of FIGS. 1 to 4;

FIG. 6 is a more detailed wiring diagram of the cycle reference channel and saw-tooth wave generator of the reproducer of FIG. 5;

7 FIG. 7 is a graphical illustration of the saw-tooth output produced by the circuit of FIG. 6;

FIG. 8 is a detailed wiring diagram of a motor control utilizing the cycle reference channel, the datum reference channel, and two of the information channels of FIG. 6; and

FIG. 9 is a graphical illustration of the variation of certain potentials in the recorder of FIG. 5.

Recording System-JUGS. J to 4 These figures illustrate the invention as applied to a system for making a reproducible record of the variations in the angular positions of two coordinately related rotating shafts. These two shafts may be the driving shafts of a tracer control system such as that shown and described in my copending application Serial No. 761,389, filed concurrently herewith and entitled Line Tracer Apparatus and Method.

In FIG. 1, the two coordinately related rotating shafts are shown respectively at 1 and 2.. The system illustrated in FIG. 1 to 4 produces a magnetic record consisting of six parallel tracks 3, 4, 5, 6, 7 and 8 on a magnetic record medium 9 which may be a conventional magnetic tape.

Fixed on the shaft 1 is a flange 10 carrying two brushes or sliders 11 and 12, angularly spaced 96 from each other, which cooperate with a circularly arranged slidewire resistor 13. A point 13a on the resistor 13 is connected through a fixed resistor 14 to the positive terminal of a direct current source indicated by the legend in the drawing as being 156 volts. A point 13b on the resistor 13, diametrically opposite the point 130, is connected through a variable resistor 15 to ground. The negative terminal of the 15 0 volt battery is grounded.

The slider M is connected through a wire 16 to an input terminal 17 of one information channel 18 of the recording system, identified in the drawings as the sine X channel. The sine X channel is shown in detail in FIG. 3.

The slider 12 is connected through a wire 1? to an input terminal 29 of a second information channel 33 of the recording system, hereinafter identified as the cosine X channel. The details of t to cosine X channel 33 are the same as those of the sine X channel 13 and a detailed description of it is considered unnecessary.

The shaft 2 has fixed on it a flange 2.1 which carries two sliders 22 and 23, apart, and both cooperating with a circularly arranged slide-wire resistor 2 One point 24a on the resistor 24 is connected through a fixed resistor 25 to the positive terminal of the l50 volt battery, Whose negative terminal is grounded. A point 2%, dia metrically opposite the point 24a, is connected through a variable resistor as to ground. The slider 22 is connected through a wire 27 to an input terminal 28 of a sine Y channel 29 of the recording system. Slider 23 is connected through a wire 3%} to an input terminal :91 of a cosine Y channel 32 of the recording system. The details of the sine Y and cosine Y channels arethe same as those of the sine X channel illustrated in FIG. 3.

The four information channels 18, 33, 2? and 32 have output terminals 18a, 33a, 2%, and 320, respectively, connected through shielded conductors to recording heads 34, 35, 36 and 37, which respectively produce magnetic records on the tracks 3%, 4, 7 and ti of the record tape g.

A cycle reference channel 38 is provided, having an input terminal 39- connec-ted to an output terminal on a datum reference channel ll. The datum reference channel 41 has an input terminal 43 connected to a Wire 44 which is in turn connected to an output terminal 45' On the cycle reference channel 35'. The cycle reference channel 38 and the datum reference channel ll have principal output terminals 386; and lla connected to the recording heads 46 and 47, which respectively produce th record tracks 5 and 6 on the record tape 9. The wire 44 connected to the output terminal 45 of cycle reference channel 38 is connected to input terminals 18b, 33b, 2% and 32b on the four information channels 18, 33, 29 and 32.

The six channels have output level setting input terminals 13c, 33c, 38c, 41c, 29c and 320, all connected to a wire 48, which is connected to a contact 49 slidable along a resistor 50' in a voltage divider which also includes resistors 51 and 52. connected in series across a direct potential supply indicated as 250 volts. A stabilizing capacifor 53 is connected between contact 45 and ground.

A coincidence indicating circuit, generally indicated by the reference numeral 54, has one input terminal 55 connected through a capacitor 56 to an output terminal 41d of the datum reference channel 41. Another input terminal 57 of the coincidence checking circuit 5-4 is connected through a capacitor 58 to a selector switch 59, by means of which it may be connected to any of output terminals 18d, 33d, 29d and 32d on the four information channels 18, 33, 29 and 32. The detailed structure and operation of the coincidence circuit 54 will be described more completely below.

FIG. 2Refercnce Channels The cycle reference channel 3 5 and the datum reference channel 41 each comprise a phantastron circuit ineluding a pentode 6d and two triodes tit and 62 which may be the tWo halves of a twin triode. The output of the phantastron in each of the reference channels drives a pulse shaper and amplifier including pentodes 63 and 64. The pulse shaper and amplifier is shown in detail only in the case of the cycle reference channel 38, and is indicated generally for that and all the other channels by the reference numeral 65.

The pentode 6t) in the phantastron circuit has an an ode Gila connected through a resistor 2% to the positive terminal of a direct potential supply indicated as volts, Whose negative terminal is grounded. The cathode 6th of'pentode d-tl isconnected through resistor 293- to. ground. A voltage divider including in series a resistor 294 and. fixed resistors 2,95, and. 295. is connected be-. tween the positive terminal of a 150 volt source. andground. The suppressor grid 6% of thepentode 6G is connected to thevcommon terminalof resistors 295 and 296 in the voltage divider. The screen grid use is connected to the common terminal of resistors 2% and 295 in the voltage divider. Note that thescreen grid is connected to a .point in the voltage divider more positive th'anthe point to which thesuppressor grid is connected. The. control grid 60 isconnected through a fixed resistor 66 and thevariableresistor 67 to the'positive terminalof-a 250 volt source. Control grid 66 is also connected through a capacitor 6310 thecathode 610 of triode61. Cathode 610 is also connected through a fixed resistor 69 to the negative terminal of a 150 volt source whose positive terminal is grounded The anode 61a of triode 61 is connected-to thepositive' terminal of the 250 volt source. Grid 61g oftriode '61 is connected through "a wire '70 to the anode-6th: of pentode 69 and also to the anode 62a of triode 62. Grid 62g of triode fi i' is connected to Wire 79; Cathode 620 of triode 62 is connectedthrough a capacitor 71 to input terminal 39 and is also connected through a fixed resistor 72.to the positive terminal of the 250"volt source.

A starting circuit is provided for they phantastron of the cycle reference channel 33. This starting circuit includes a capacitor 73 andapushbutton switch 74biased to a position where itshunts the capacitor 73 and movable to a starting position where it connects the capacitor 73 between the wire 70 and ground.

Two-stage amplifieroS is for the most part conventional,- and-Will. be described" only briefly; The output of the phantastron pentode 66- is coupled fromthecommon junction of resistors 7.94am 295 through a capacitor 75 to an input terminal 76 and thenceto the control grid-63f of the pentode 63. Pentode 63 is connected iua pulse shaping stage, generally similar to the phantastron circuitincluding pentode 65 This pulse-shaping stage converts sharply peaked output pulses from the phantastron to square topped pulses of fixed predetermined duration.

Grid 63 and anode 63a are coupled through a ca pacitorw'i. Anode 63a is connected to the positive terminal of the 150 volt DC. source through a resistor 85; Input terminal. 76 is connected through a fixed resistor 86 and a. variable resistor 87 to the positive terminal of'the. 150- volt DC. source. A voltage divider comprising resistors iifi, 89 and 90 in series is connected across the 150 volt DC. source. Screen grid 63a and suppressor grid 63d are connected respectively to more positive and more negative points on the divider 85, 89, 99. Theqcathode 63c ofwpentode 63' is connected through a. resistor '77 to ground and is also connected through. a wire 73 to the output terminal 45. Screen grid 63a is connected to a'checking output terminal 38d (not-used in the cycle reference channel 38; although correspondingterminals are used 'in all the other channels);

The output of'pentode 63 is taken from the screen grid 63c through a capacitor '79 and a resistor Sti to the control grid 64f of the pentodee l. Pentode 64 .is connected as a power amplifier stage. The screen grid Me of pentode 64 is connected. to theoutput pulse level setting input terminal Shc. The anode 64a of pentode 64 is coupled through a capacitor -81 to the-principal output terminal 38a and thenceto the recording head 46. Anode 64a. is connected through resistors 91 and 92 to the positive terminal of a 300 volt D.C. source. The cornmonterminal of resistors 91-and92 is'connected'to groundthrough a capacitor 93.

Operation of Reference Channels- Thei-phantastron is a Well known type of time delay:

received at the terminal 39; Thetriode 61 is-acoupling;

triode used in place of a more conventional high resistanceto couple'the anodeiia of-pentode 6ti-to the capacitor68"withoutthe risk of loading the anode 6%:

which is encountered'iin: the morev conventional circuit.

In. its. quiescent or'steady state condition, the control" gridioii-fof pentode 6%. is held near zero bias, i.e., its:

potential is held close to the potential. of cathode: 60c, by .the -fiow of grid current, .since' it is connected through the resistors-and ()7 to the high positivepotential.

source. Thescreen gridide isconnectcd to a point on the voltage divider which ispositive withrespect to the cathode 68c so that that grid is drawing substantial. cur-v rentalso. The suppressor grid. 60d is connected to a point on' the voltage divider-which is-negative with respect tothe cathode sothat the grid 6011 is effective to cut ofl'the anode current. Thecurrentflowing through the cathode 600 is principally screen grid current. Since the cathodeo z'c oftriode z is held at 250 volts while its anode is held at volts, that triode is'not conductive;

With the phantastron -6ti' inits steady. statecondition, assume that a negative going'trigger pulse is supplied tothe wire-7t). This may be supplied either through inputterminal 39 and capacitor--71, thereby making the triode z momentarily conductive, or it may be supplied by a momentary closure by-the switch 74 'inits starting position.- This negative pulse is transferred to the anode 60a of pentode-1 team through the grid 61g and cathode- 611: of triode Glto the capacitor 68 and through that capacitor to the control gridj 60f of pentode 66. This negative going pulse appearing at the control grid duf decreases thecathode current and thereby decreases the potential dropacrossthe cathode resistor293. Hence the cathode potential is lowered, and-the suppressor grid 60d, Whose potential is fixed, becomes' less negative-With respect to thecathode. The potential of grid dtid'is setso: that when the cathode 6d swings. in the negative direction, anode current starts to flow; This'currentflow through. resistor 292 causes the potential at anodefifi'a to drop, cutting oil the conduction in'the triode.62'. This droprin potential istransferred through grid 61g and cathode 610 to the capacitor dhtandth'ence to. the control grid 6%.

This initial change takes place before capacitor 68 changes its initial charge appreciably. The capacitor now starts to dischargeand in so doing raises-the-potential of the control grid 60 This increases the current through anodefiiirt which decreases the potential at anode 643a which decreasing potential is transferred through triode 61 and capacitor '68: to the control grid- 66f. Thus two opposing actions are established, namely thedischarging of the-capacitor 68', which tends to increase thepotential of grid 69f, and the lowering of the-potential o-f anode 69a, which tends to decrease the potential of grid 60 There-results a very slow decreasein anode potential and an increase in cathodepotential, these changes being sub stantiallylinear with 'time. These effects continue until the anode and screen voltages are so lowth-at a further increase in the voltage at'grid fitifdoes not increase the anode current. The grid 60 and consequently the cat-hode, continue to increase in potential for a short time withthe screen taking the increase in'the cathode current. Grid 60d then becomes effective to cut the plate current off With 'a consequent sudden rise in the anode voltage. This" rise in voltage is'fed back to the control grid ear; bringing the circuit back to normaL' This suda den rise in potential at the end of the cycle is shaped and amplified by the pulse shaper and amplifier 65, to which it is transmitted through capacitor 75, being derived from the sudden change in the potential of the screen grid 602 at the end of the cycle.

It may thus be seen that the phantastron establishes a closely controlled time interval between an input pulse received at terminal '39 and an output pulse appearing at amplifier input terminal 76. This time interval is established by the fixed circuit parameters and is substantially unaffected by fluctuations in the voltage supplies during the intervals being timed.

The amplifier 65 is provided with three output terminals 3&2, 45 and 33d. Terminal 38a is the principal output terminal and is connected to the recording head 46. Output terminal 45 supplies triggering pulses to the datum reference channel and to all the information channels as Well, as will be described below.

Terminal 38a is not used in the cycle reference channel 38, but the corresponding output terminal is used in all the other channels in connection with the coincidence checking circuit 54. Terminal 38d is connected to the screen grid 63c of the pentode 63.

The phantastron in the datum reference channel 41 derives its input pulses from the output terminal of the phantastron in the cycle reference channel 38. Similarly, the phantastron in the cycle reference channel derives its input pulses from the output terminal 49 of the datum reference channel 41. Consequently, it may be seen that the phantastrons in these two channels constitute a multivibrator or trigger, each producing output pulses after specific and accurately controlled time intervals. In FIG. 4, the output pulses of the cycle reference channel 33 are shown by the reference numerals 82a, 82b and 820. The output pulses for the datum reference channel 41 are shown by the reference numeral 83.

Referring to FIG. 4, the complete time interval there illustrated is divided into three cycles 84. The cycle reference pulses it-2a, 82b and 820 mark the beginning of each cycle. The datum reference pulses "83 marl; the center points or median times of each cycle. The phantastron of the cycle reference channel 38 and the datum reference channel 41 may be aligned to bring the datum reference pulses 83 exactly halfway between the cycle reference pulses 82a, "82b and 82c by comparing their outputs on an oscillograph and making necessary adjustments in the variable resistors 67 of the two phantastrons.

The frequency of the trigger constituted by the cycle reference and datum reference channels is preferably made high as compared to the frequency of variation of the input signals, represented in the apparatus shown by the frequency of rotation of shafts 1 and 2.

FIG. 3-Inf0rmation Pulse Recording Channel This figure illustrates the details of one of the information channels, specifically the sine X channel illustrated at 18 in FIG. 1. All the other information channels are essentially the same as this one. The initial stage in the information channel is a phantastron circuit including a pentode $4 and two triodes 95 and 96. The anode 94a of pentode 94 is connected through a resistor 97 and a Wire 98 to the input terminal 17. It may therefore be seen that the anode potential supply for the pentode 94 is derived from the slider 11, and varies sinusoidally with the angular position of the shaft 1.

The cathode We of pentode 9'4 is connected through a resistor 99 to ground.

The control electrode 947 of pcntode $4 is connected through a fixed resistor 1% and a variable resistor ltll to the positive terminal of a 250 volt D.C. source. Control electrode 94 is also connected through a capacitor M2 to the cathode 95c of triode 95. Cathode 5c is also connected through a resistor 1113 to the negative terminal of a 150 volt 11C. source. Control electrode 95g of triode 95 is connected through a wire 194 to the anode 94a.

f5 Wire 164 is also connected to the anode 96a of triode 96 and to the control electrode 96g of that triode. Anode a of triode )5 is connected directly to the positive terminal of the 250 volt source. Cathode @60 of triode 96 is connected through a capacitor 165 to the input terminal 1% supplied by the cycle reference channel 38. Cathode $60 is also connected through a resistor 106 to the input terminal 17. The latter terminal is also connected through a capacitor 2% to ground.

A voltage divider including three resistors 107, 1&8 and 199, connected in series, is connected across the terminals of a 150 volt DC. supply. The screen grid 94c of the pentode- 94- is connected to the common junction of resistors 107 and 198. The suppressor grid 94d of pentode 94 is connected to the common junction of resistors 108 and res. Screen grid 94a is also connected through a coupling capacitor 110 to the input terminal 76 of a pulse shaping and amplifier circuit 65, which corresponds to the pulse shaping and amplifier circuit 65 of FIG. 2. The information channel 18 is provided with a principal output terminal 18a and a checking output terminal 8d. Au output pulse level setting input terminal is also provided.

Operation 07 Information Pulse Recording Channel As the shaft 1 rotates, the potential at the slider 11 varies sinusoidally as a function of the angular position of the shaft. In the quiescent condition of the phantastron circuit, there is no current flow through the anode 94a, so that the anode potential follows closely the variations in the slider potential. Cathode this is connected to the anode 96a through the resistors W6 and 97, so that they are both at the same potential and there is no current flow through the triode 96. Triode 96 is connected effectively as a diode. Resistor 106 has a high resistance (1 megohm).

The potential of the slider 11 varies over a limited range located between volts and 0, the exact range being determined by the setting of variableresistor 15. The resistors 13, 14 and 15 are so chosen that the most negative potential appearing at the anode 94a, due to changes in position of slider 11, cannot be effective to trip the phantastron.

If a negative going input pulse is now received at terminal 18b, having a value sufiiciently large, it will pass through the triode 9'6 and be applied to anode 94a and also through the triode 95 and capacitor 1% to control grid 94]. The magnitude of the input pulses so transmitted is sufiiciently large to trip the phantastron and start it running through its timing cycle as described above in connection with the phantastron pentode 60 of FIG. 2. However, the timing cycle of the phantastron 94 of FIG. 3 is not of fixed duration, but depends upon the potential on the anode 94:: at the time the phantastron is tripped. During the timing cycle of the phantastron, its anode potential continuously decreases as a linear function of time. The cycle ends at a fixed value of anode potential, hereinafter referred to as the signal output level 114- (FIG. 4), determined by the tube characteristics and by the connections of the grids 94d, 94:: to the voltage dividers 167, 1%, 1159. Consequently, the potential at the anode at the tripping instant determines the time it will take for the linearly decreasing potential to reach the end of its cycle, at which time it produces an output pulse signal. Hence, the time elapsed between the tripping pulse and the output pulse in a linear function of the potential at slider 11, at the tripping instant.

When the slider 11 is at the junction 13a, the phantastron anode potential will be at its most positive value. The variation in the plate voltage of the phantastron is illustrated in FIG. 4 by the curve 111 through three cycles of operation, respectively identified as cycles 84a, and Me. At the instant when the cycle reference pulse 82a is received during the cycle 84a, the potential of the slider 11 illustrated at the curve 112, is at its max- 9*. imum value. The. phantastron output potential. then follows the curve ,111 through thecycle 84a, reaching its. signalou-tput level, at thepoint 111a. producesanoutput pulseat that point, which is shaped by the pulseshaper and amplifier 65 and. is fed to the recording head.34 asa square wave output pulse 113a.

Considering now thecycle 84b, assume that the slider 11 is. at a. position half-way between the junctions 13a and 13b, sothat its potentialis at the median value of its-range. The anode potentialofthe pentrode 94 now follows the. curve-111 th'roughthe cycle 84b, producing an output pulse beginning at time 111b, the mid-point of the cycle.

Consideringthe cycle 84c, it isassumed that the slider 11 is in con-tact with the junction 1321 when the cycle reference pulse82'c is received. The phantastron. proceeds through its timing cycle as before, but now starts at an anode voltage only slightly higher than the. output level 114, so that the output pulse is produced at -a time 1110.

The entire lengthof the cycle 84a,'84b-or 84c cannot be usedfor the transmission of information, if accurate transmission throughout the full potential range is to be obtained. A sufficient time must. be allowed after the point 113a (corresponding to a maximum input potential) for the phantastron pentode to assume its quiescent condition before the. next cycle is started by. the cycle reference pulse 82b. Similarly, at. the minimum potential as shown in cycle 840, the phantastron must go through a cycle ofja'finite time before producing its uoutput pulse. Because of these two factors, the transmissionof informa tion in each cycle is accomplishedonly during an intermediate'interval of the cycle illustrated by the reference numeral 115 in FIG. 4 and referred tohereinaft'er as the coding intervaL. The coding interval '115is precededby a preliminary interval 116'which.is required for the minimum signal and is followed within the cycle 84 bya short final interval 117 during which'phantastron circuit and the pentode 94-are returning to their quiescent states.

Coincidence. Circuit 54'Calibration-FIG.1

In order that the times of the output pulses 113a,.113b and 1130 may represent specific potential values, it is necessaryto establish a fixed datum relationship between a particular time within the coding interval 115 and a particular value of potential. In the system described, the datum potential-time relationship is established by ad? justing the information channels so that when their respective input potentials are at their medianvalues, those channels produce information output pulses 113b which are coincident with the datum reference pulses 83, which occur at median times within the coding intervals 115. This adjustment of the respective information channels maybe accomplished with the aid. of the coincidence circuit 54 and the selector switch 59, shown in FIG. 1.

The coincidence circuit 54 comprises a pentode i121) and two tri'odes 121 and 122. The anode 12la of'pen-. tode l2d is connected through'a resistor 123 to the positive terminal" of the 150' volt supply. Cathode 1211c is connected through resistors 124'and'125 to ground. A capacitor 291 bypasses the resistors 12d and 12$. The common junction'of resistors 124 and 125 is connected through "a resistor 129*to the positive terminal of the. 150

volt supply. The control grid 120d is connected to the input terminal 55 of the coincidence: circuit. The sup: pressor "grid 121) is connected tothe input terminal 57 and thence throughcapacitor 58*to the selector switch Screengrid 12% is connected to the common terminal of resistors 126-and 127, which are connected across the 150 volt supply andserve as a voltage divider. A capacitor 128 is connected in, parallel withtresistor 127. Screen grid 12% is also connected through a coupling resistor 130 to the control grid 121b of the triode 121. Control grid 121bis. also connected through a .resistor 13*3to ground; The anode 12142 of triode 121'is connected through a wire 131 to the anode 120a of pentode The phantastron.

. 10 121i and through a capacitor 132 to the control grid 12% of triode :122. Control grid 122i; is connected through a resistor 134 to cathode 122C. The cathodes 121C and 1226 are connected together and through the resistor 135 to ground. Anode 122a 'oftriode 122 is connected through. a resistor 136' to the positive terminal of a 250 volt source. are connected in series between the anode 1226i and ground.

Operation of Coincidence Circuit The triode 122 is normally conductive so that the neon lamps- 137 and 138 have a potential drop; across them lower than the threshold: voltageat which they beginto glow. The lampsare therefore normallynot illuminated. Such lamps characteristically have to.be supplied with energizing potential a greater than the threshold voltage for a predetermined time before they will produce a visible flash.

The potential drop across'resistor 135 due to the cur-i rent flowing through triode .122 holds .thecathode 1210 sufiiciently.positivewith-respect-togrid:12112 so that the triode-121 is cutoff. The potential-ofgrid121b and of screen .grid121le is determined by the voltage dividers 126, 127."

The pentode. rris normally non-conductive. The potential of cathode 1211c isiestablished by the voltage divider 1'29, 12$.substantially. above ground potential; The suppressor grid 12% is connected to ground through resistor .139. The control electrode 12% is connected to ground through a resistor140;

The pentode 120 will not conduct current through its anode unless simultaneous positive going-pulsesare received simultaneously at thecontrol grid 12% and the suppressor grid 120 The pulses at the control grid 120d are determined by the datumrefe'rence channel 41 (see FIG. 2), and occur exactly halfway between the cycle reference pulses 82.

It is desirable to :adjust the-sine X channel 18, shown in detail in FIG. 3; so that when the slider 11 is at the midpoint of'resistor'lfi, halfway between the junctions 13a and 1312, the output pulses from channel 18- will occurcoincidentally with the datum pulses 83 from the datum reference channel 41.

To accomplish this end, slider '11 is set at the midpoint of resistor 13, andthe selector-switch is set at the contact 5961, which is connected to the output terminal 18d of the sine X channel-18.- The resistor 15 is then varied in value until the neon glow lamps 137 and 138 flash. This indicates that the pentode 121]- is receiving input pulses simultaneously from the datum reference channel at input terminal 55 and from the sine'X channel at the input terminal 57.

When such simultaneous pulses are received at the two inputs of the pentode 120, it conducts a pulse of anode current. A negative going pulse appears at the anode 120a and is transmittedthrough wire 131 and capacitor 132 to the control grid 1222b of triode 122, cutting that triode off. The potential drop across resistor suddenlydisappears, and thepotential of cathode 1210' momentarily becomesequal to ground potential. Since thisis below the potential of control grid 121b, the triode I 121 starts conducting. During the pulse through pentode 121), the screen grid 120a conducts substantial current, and its-potential, swings negative, the negative swing charging the capacitor 128 partially and lowering the potential of the control grid 121b. In order to restore conditions to normal after the pulse through pentode 12d terminates, the capacitor 128 must regain its previous charge through the resistor 126- and capacitor 122 must charge through the resistor 134. The latter is a high resistor (1 megohm). As long. as triode 121 remains conductive, there is only a low potential applied across capacitor 132 and resistor 134, so that it. does not reacquire its normal charge rapidly. As triode 121 continues to conduct, the capacitor 128'is gradually charged,

A pair of neon glow lamps 137and 13, 8

so that the potential of control electrode 12117 returns to its normal value. This increase in the potential at the control grid 1215 increases the current flow through resistor 1Z5", thereby raising the potential of cathodes 1210 and i220. Eventually a point is reached where the control electrode 12% is at a stable potential and the current flow through triode .121 no longer increases. The capacitor 132 gradually charges, and as it charges, the anode potential of triode 12 1 is increased. Eventually, triode 122 comes on again, and its increased current flow through resistor .135 swings the cathode 121a more positive than control grid i211) and cuts triode 121 off.

The input pulses from the reference channels and from the information channels are of too short a duration to light the neon glow tubes 1.37 and 138 for a long enough time to be visible by the operator. The triodcs 312.1 and 22 together form a single shot trigger having a normal condition in which the tube 122 is conductive and shunts the glow tubes 137 and 138. When the trigger is tripped by the pentode 12 3, it shifts to its opposite condition where the triode 122 is cut oh and the triode 12]; is conducting and maintains that condition for a time determined by the characteristics of the circuit constants especially capacitor 132 and resistor 134. This time is long enough so that the glow tubes 137 and 133 become illuminated long enough to indicate to the operator that the output pulses through the sine X channel 13 are synchronized with the pulses from the datum reference channel 41.

A single information channel, such as the sine X channel, may be used together with the cycle reference channel 3d and the datum reference channel 41 to produce a three-channel magnetic record of any variable potential which is fed into the input terminal '17 of the channel 13. This potential may represent any particular intelligence which it is desired to record. In the present instance, the potential is an indication of the angular position of the shaft 1.

By using two channels, such as the sine X channel 18 and the cosine X channel 33, along with the cycle reference channel 38 and the datum reference channel 41, signals are recorded which indicate not only the angular position of shaft 1 but its direction of rotation at any particular instance. Furthermore, the sequence of potentials obtained from the sliders 11 and 1?. as the shaft it rotates provide information from which the speed of rotation of the shaft 1 may be derived.

By utilizing in addition the sine Y channel 29 and the cosine Y channel 35, the angular position, direction and speed of rotation of the shaft 2 may be recorded simultaneously. The complete record, including all four information channels, may be used as the record of the outline of a pattern traced by a tracing mechanism such as that shown and described in my copending application Serial No. 761,389, filed concurrently herewith and entitled Line Tracer Apparatus and Method. 7

It may be seen that there is a fixed time relationship between the cycle reference pulses 32 and the datum reference pulses 83. In view of this fixed time relationship, it may appear that only one set of these pulses is necessary for the recording of data or information. In some systems embodying tie broader aspects of the invention, it may be possible to omit one of these two sets of pulses from the recording.

However, as will be understood from a consideration of the description of the reproducing method and apparatus, which appears below, if the cycle reference pulses are omitted from the record, then those pulses must be reconstructed at the reproducer from the datum reference pulses $3. While this is entirely possible, it complicates the reproducing mechanism to such an extent that it is simpler to record the cycle reference pulses on a separate track of the recording medium.

It is essential that one set of the fixed time pulses have a positive datum relationship to a fixed value of potential.

If the datum reference pulses 33 are omitted, then that fixed time-potential relationship must be established for the cycle reference pulses 82. As explained above, since these occur at one end of the recording cycle, they must coincide with one particular end of the range of potentials being recorded. Furthermore, because of the less stable conditions in the phantastron circuits at the ends of the cycle, the potentials recorded would be subject to inaccuracies as their value approached the particular end of the range represented by the cycle reference pulses 82.

In a system for transmitting a single variable potential on a single information channel, it might be possible to omit the datum pulses 33 and to use in the reproducer a datum potential having a fixed value, e.g., ground. However, such an arrangement would be subject to further in accuracies in the reproducer as described below.

The system described using both the cycle reference pulses 82 and the datum reference pulses 33 has the advantage of providing an accurately reproducible calibration of time and potential, with a simple reproducing mechanism. Furthermore, by using the same calibration for all the information channels, it is possible to accurately reproduce a plurality of related variables in their proper relationship to one another.

Reproducing Apparatus-FIGS. 5 l0 9 The reproducing apparatus is illustrated diagrammatically in FIGURE 5. As there shown, the magnetic tape 9 or other magnetic recording medium, carrying the channels 3, 4;, 5', 6, '7 and 8 is driven by suitable mechanism, which may be conventional, past a series of pickup heads 14-1, 142, M3, 144-, 145 and 146, one for each of the six channels.

The several pickup heads are respectively connected to channel amplifiers 147, 143, 149, 156, 151 and 152. The

channel amplifiers take the pulses received from the pickup head, which pulses may have a rounded contour and whose amplitude may vary somewhat, and, by means of suitable pulse shaping, amplifying and clipping circuits, convert those pulses into square wave output pulses of fixed amplitude and fixed duration. These amplifiers do not, however, affect the timing of the pulses relative to each other. Since it is by this timing that the intelligence is transmitted, that intelligence is not disturbed by the action of these amplifiers.

The cycle reference channel amplifier 14% produces a series of square wave output pulses, such as shown at 153 in FIG. 9. The pulses 153 are fed to a saw-tooth generator 15 shown in detail in FIG. 6, which produces at its output terminals a saw-tooth wave having a contour illustrated at 155 in FIG. 9.

The datume reference channel amplifier ldtl produces a series of output pulses 156 (see FIG. 9) which are spaced at the midpoints of the cycles defined by the cycle reference pulses 153.

The several information channel amplifiers 147, 143, 151 and 152 produce output pulses whose spacing or timing with respect to the datum pulses 156 varies as a function of the electrical potentials recorded on the record medium 9. One set of such pulses is shown at 157 in FIG. 9, and includes two pulses 157a marking the maxi mum value of the record potential and two pulses 1571) marking the minimum value of the recorded potential.

The saw-tooth Wave 155 produced by the generator 154 is fed to a saw-tooth input of each of a series of five sampler circuits 153, 1559, 160, 161 and 162;. Each sawtooth input terminal is identified by the reference numeral of its sampler circuit followed by the letter a. One sampler circuit is provided for each of the five channels other than the cycle reference channel. The sampler circuits for the sine X information channel and for the datum reference channel are shown in detail in FIG. 8. In each of the samplers, the saw-tooth wave is sampled at the instants determined by the times of the information pulses received from the associated channel amplifier. Each channelamplifier-is connected to an information pulseintput'on its associated sampler, which input is identified by.

the reference. numeral-of the sampler followed by the letter--b. Thecutput of-the. datum reference channel sampler 160 is-fed to a comparator.- 2l9*(shown in.detailin FIG. 8'), which producesa potential equal .to the-sampler output, but which; is dynamicallyst-abilized and stored on 1 thecapacitor163.-

The outputs :of each of the information. channel samplers 158,159, 161 and-.1 62:ar e fedtorespective compara-: tor; circuits 164,165, 1-66 =ancl7167- (comparator. 164 is The1outputsof the-comparashown in detail in FIG. 8 tor circuits, are fedto' power amplifiers 168 169, .170 and 171.

The power amplifiers-168 and169-control .the. supplyof energy to an X'direction-motor 172, which-may be of the split phase-type, the" currents in its. respective phase: windings being; supplied-by the two; amplifierss 1 6 8 and 169. The currents in the respective phases are sampled by feedback; samplers= 173',: 174,; ,175 :andv1716,. and-the outputsofjthese respective feedback samplers'are stored:

of related variables, as it does in the case; of thezsine X',

sine. Y, cosine X'and cosine Y. channels. of:the tracer control system illustrated, it is necessary that all the: potentials be related to a single datum potential 'in order that the variations of the several information. potentials with respect to each other maybe properly .recordedand' reproduced. However, in the windings of the X- and.Y motors 172and 181, thedatumwpotentials have no signifi-. canoe. Those motors are controlled only by the variations of the sine and cosine signals with respect to each other. The output signals from the samplers 158- and 15-9, for example, are composite signals including a component due to the datum potential and a component reproducing the variation of the information potential. By adding the datum potential to'the input at the feedback side of the comparator, the comparator outputis made to represent accurately only that portion'of the input signal which is-concerned with variations in the informa-. tion potential. Thus the motor receives in its two winds ings only the information potentials which are significant to its operation.- If the datum potentials were fed to the two windings of the motor they would tend to buck each other and reduce the sensitivity'of the motor to changes in the information potential.

Saw-Tooth Generator-FIG. 6

The saw-tooth generator shown diagrammatically at 154 in FIG. is shown in detail in FIG. 6. It includes a phantastron stage 182 including a pentode .183 and a diode.184.- The,.phantastronstage 182 has its.output connected to oneahalf 2%1- of a twintriode 185, which serves as an amplifier. The other half 205 ofathe twin triode v185 is connected in-series witha pentode 186and in parallelwith a capacitor 187; in asaw-tooth generating stage generally indicated bythe reference numeralilstl- The output of the saw-toothgeneratingstage 188 .is fed to a triode. 189m an-inverted'amplifier stagev generally indicated at-190. The output ofthe amplifier stage 1-90- is fed to the input. of a power amplifier stage191--including a beam power tube 192. A feedback is provided from theamplifier, stage-i to the pentode 186 through, adiode 193 and aparallel resistor 194 and capacitor 195'.-

The phantastron stage,182 primarily serves a pulse shaping. function. It.receives a negative going input pulse, indicated.diagrammatically at 196in the drawing, and .converts it into another negative goinginput, pulse 197'having afixed. duration somewhat shorter than the. interval 116.between the. beginning. of the cycle and the.

beginning of thecodingzone, as illustrated in FIG. 4.

The details ofthisphantastron stage are for the most part similarto that offthephantastron stage described above; in connection with..FIG. 2 and such details will not be furtherdescribed... The. cathode 1830 of pentode 183is. connected to. ground through a resistor 198. The

output of the phantastron. stage .is takenacross the resistor 198. The cathode.183c.is connectedthrough a coupling.

resistor..199 andaparallel capacitor 200 to the control grid 201g Ofthefirst half 201.0f the twin. triode 185.

This triode has its-cathode. 2010 connected to ground through avariableresistor.202.and aparallel capacitor 203;- The triode. 201 draws sufiicient grid. current to build up on capacitor 200a potential. eifectiveto. bias the triode 20-1:to a stablequiescent statewhere it. is carrying substantial current... Anode 2tl1a of triode.2tl1.is-

connected. througha resistor 284 :tothe positive terminal of a 150tvolt. D.C. source. The control electrode 205g of thesecond. half 205. of .the twin triode-185. is con-- nected. to. the. anode 201a.-

At the beginning ofa cycle, the capacitor. 187v is charged and'the controlelectrode 205g is at a sufficientlylow. potential due. to'the current through resistor 264 so that triode 295 is cut off. When a negative going pulse-197:

is received: from-the phantastron stage 182, it is effective.

to cut-01f the triode 201, thereby terminating thecurrent flow through resistor 204. and swinging the grid 205g. strongly positive. The triode 265 thereby becomes a direct shunt on the capacitor. 187; discharging it quickly. The potential of grid 189g-0f triode 189 is thereby swung. strongly positive so that triode 189- conducts current at a high rate, producing a substantial potential drop across.

resistor .266, connected between anode 139a andthe positive terminal ofthe 1S0v volt source. Thepotential at anoder 189ais transmitted through: a coupling resistor. 26.7 and a variable resistor ZtlStothecontrol electrode 192g of thepower tube 192.

Triode 189" is connected as a cathode follower and has resistors 2M and Ziticonnected in series between its cathode. 189a and the negativeterminal of a 1-05 volt bat.- tery. The common junction of. resistors 269 and filth-is connected throughthe "diode193' to the control grid 186g of the pentode 186. The screen gridnl8ae of the pentode 186 is connected to the: cathode 2031c of triode 201. The suppressor grid 186d of pentode 1864s connected in a conventional fashion to the cathode 186a.

The-pentode :186is arrangedfor constant current operation, as is conventional with such-pentodes'in.sawrtooth generator circuits.- The potential of the screen grid186e, taken'across resistor 2%, is stabilized by thev capacitor 203 so that it is-substantially constant duringtheintervals' when triode 201 is cut off. The circuit constants are chosen so that the screen grid potential is quitelow. (around +20volts) so that the controlgrid 186g has a strong influence on the current flowthrough'the pentode 186 (control grid lfifigshould have about a 2, volt range between cutoff and full conductivity of the pentode 186).

After the capacitor 187 is discharged at the beginning ofthe cycle,; theinput pulse-terminates and triode 201 againqbeginsto conduct current and cuts off the triode 205.: Capacitor 187- starts tocharge through'the anode? cathode circuit of pentode 187, which as stated before, is arranged to conduct a constant current. The-potential across. capacitor-187 therefore begins to riseina linear relation with time. This relation increases. the current flow through triode 189 linearly withtime and thereby decreases the potential 'of anode 189a linearly with time.

spea s-es The saw-tooth wave appearing at the output of triode 1&9 may therefore be described as a sudden rise of potential followed by a linear decrease. This wave is fed to the control grid 192g of the power tube 192.

As the current flow through the triode 189 decreases with time, the potential of cathode 189s swings negatively toward the potential of the 105 volt battery. At a predetermined potential, which is established principally by the characteristics of the resistor 19 i and capacitor 195', the potential of the junction between resistors 2G9 and 210 swings below the potential of the grid 135g and the diode 193 conducts, thereby supplying an additional charge to capacitor 1%. When the circuit is running in a stable manner, the additional charge supplied to capacitor 195 during each cycle is just sufficient to balance the leakage of charge through resistor 194-, so that the potential of grid 136g remains substantially constant. If for any reason the capacitor 187 charges too rapidly, (due perhaps to too high a potential on the grid 186g), then the critical potential is reached more quickly and the capacitor 195 receives an additional charge at the end of the cycle so that the operation of the charging capacitor 187 is corrected on the next cycle.

It may be seen that the upper limit of the swing of the control grid 189g is the potential of the positive terminal of the 150 volt battery, which is fixed. Also, the lower limit of the swing of that potential is restricted to a range of 2 or 3 volts by the action of the feedback circuit 193, 194 and 1195. Consequently, the saw-tooth wave appearing at the input of the triode 189 has a substantially fixed amplitude. This amplitude is maintained substantially the same regardless of the frequency of the input pulses received from the pickup unit 143. As explained more fully below, this substantially constant amplitude ensures that the output potential supplied to the X and Y motors are faithful reproductions of the potentials recorded, regardless of the variations in speed of the record track past the pickup units 143. The circuit described has been operated with a range of variations of to 1 between the maximum and minimum tape speeds past the reproducer head, without substantial variation in the pattern reproduced.

The resistors 267 and 208 are connected in series with the resistor 2th; and a resistor 211 to form a voltage divider which sets the potential level of the control grid 192g. A feedback is provided from the anode 192a of the power tube 192 through a resistor 212 to the cathode 1890. A capacitor 2% couples the anode 192a and the control grid 192g. The anode 192a is connected through a load resistor 213 to the positive terminal of a 400 volt DC. source. A voltage divider including resistors 214 and 215 in series is connected across the 400 volt source. The screen grid 19% of the power tube 192 is connected to the common junction of the resistors 214 and 215. The output of the power stage 11 is taken from the anode 19201 through a wire 216 and is delivered to the sampling inputs of all the samplers 158 to 162, as shown in FIG. 5.

The power stage 1&1 inverts the output from triode 139, so that the final saw-tooth output wave is a sudden drop in potential followed by a linear rise.

FIG. 7 illustrates diagrammatically that the saw-tooth stage 18% produces a saw-tooth wave 217 whose amplitude is substantially constant regardless of variations in the frequency of the saw-tooth.

Reproducer-Jiatum Reference Channels and Information Channels-FIG. 8

This figure illustrates the details of the sampler circuit res and comparator circuits 164 and 219 which are shown schematically in FIG. 5, and the connection of those circuits to the control of the X motor 172.

Considering first and datum reference channel, the signal from the datum reference amplifier 150 is received at an input terminal 16%. The saw-tooth wave from the generator 154 is received at an input terminal 16%. The

sampler 164 samples the saw-tooth wave at the instants marked by the amplifier 159 and stores the sampled value on a capacitor 218. Comparator 219 compares the potential on capacitor 218 and dynamically supplies an equal and balancing potential on a capacitor 163. The comparator serves to maintain the potential on capacitor 163 equal to that on capacitor 218, without substantially loading the generator 154 which must supply the energy for charging the capacitors 218 in the samplers of all the channels. The potential on capacitor 163 is backed by the power supply of the final stage of the comparator and so can supply a substantial load without significant variation of the stored potential.

The sampler 160 comprises a blocking oscillator including triodes 225 221 and 222. This blocking oscillator responds to the input datum pulses and produces sharply peaked output pulses which are fed to the grids of a pair of triodes 223 and 224, connected back-to-back in series with the output of the saw-tooth generator 154 and the capacitor 218.

The input pulses reaching the terminal 16% are connected to the control grid ZZtlg of triode 229. The anode 22% of triode 220 is connected through the primary winding 225 of a transformer 226 and a resistor 227 in series with that primary winding to the positive terminal of the 150 volt DC. supply. A secondary winding 228 of the transformer 226 has one terminal connected to the control electrode 221g of triode 221 and its other terminal to ground through a resistor 229 and a parallel capacitor 23-8. The latter terminal is also connected through a resistor 231 to the negative terminal of a volt battery supply which serves to bias the triode 221 off. The triode 222 is connected as a diode in parallel with the primary winding 225 and serves to shunt the winding 225 during the negative going half of the peak, so as to make the peaked output sharper.

When an input pulse is received at terminal 16Gb, it is transferred through triode 220 to primary Winding'225, and is fed back through winding 22% so as to drive the grid of triode 221 positive and produce a sharply peaked wave in the primary winding 225.

The transformer 226 has secondary windings 232 and 233 respectively connected in the grid circuits of triodes 2 23 and 224. The connection is arranged so that regardless of the polarity of the output of the saw-tooth generator 15d with respect to capacitor 218 at any instant, when the blocking oscillator produces an output pulse, one of the triodes 223 and 224 becomes conductive and thereby stores the potential from the saw-tooth wave on the capacitor 218. The saw-tooth generator 154- must drive capacitors 218 in the datum reference channel and all of the information channels. The beam power output stage 191 (Fl-G. 6) of the saw-tooth generator is provided to carry that load.

The potential on capacitor 218 is fed to one side of a comparator or balancing circuit 219. The comparator 219' comprises two triodes 234 and 235 having their cathodes connected to ground through a common resistor 236. The anode of triode 234 is connected through a resistor 23"! to one terminal 'of a resistor 238 having a movable center tap connected to the positive terminal of a 400 volt DC. supply. The anode of triode 235 is connected through a resistor 239 to the opposite end terminal of resistor 238. The anode of triode 23a is also connected through a resistor 240 to ground. The anode of triode 235 is connected through a resistor 241 and a resistor 299 to ground. The common terminal of resistors 241 and 299 is connected to the control electrode 242g of a triode 242. Triode 24-2 is connected as a cathode follower, having its anode directly connected to the positive terminal of the volt DC. supply and having its cathode connected through a resistor 243 to ground. Capacitor 1% is connected across the resistor 2 93. The ca bode of triode 242 is also connected to the control electrode 245g of triode 245.

The comparator 219 is used to maintaina balance between the potentials of the control electrodes 234g and 235 If that balance is upset, for example, by an increase in the potential at electrode 234g, .then the current flow through triode 234 increases, raising the potential of the cathode 234s and 235a and tending to decrease the conductivity of triode 235. This increases the potential of anode 235a, and the increase in potential is supplied to grid 242g of the cathode follower 242, thereby increasing the current flow through that tube and driving its cathode more positive, carrying the grid 235g more-positive until a balanced condition is reached. If either triode 234 or 235 carries more than half the cur- .rent flow through the resistor 236, an unbalance occurs in their anode potentials which tends to produce a balancing reaction. The result is that the capacitor 163 is maintained at a potential equal to that across the capacitor 213. The potential is maintained with substantial power provided by the cathode follower 242, so that any load connected to the capacitor 163 is compensated and the potential is not substantially reduced or increased by variations in that load.

The sampler circuits 158 and 159 are essentially the same as the sampler 160' described above. The output terminal 15530 of sampler 158 is connected to a comparator 164 which is broadly the same in its function as the comparator 219, but is specifically different because of the fact that it has to balance a wider range of input potentials. The input potential at terminal 1649c to the comparator 219 does not vary over more than 2 vol-ts Whereas the potential at terminal 15% may vary, for example, over a range of from 55 to 140 volts.

The comparator 164 comprises two triodes 244, 245 having their respective anodes .connected through resistors 2146' and 247 to the positive terminal of a 400 volt D.C. supply. Their respective cathodes are connected through resistors 24% and 249 to ground. The anode of triode 244 is cross-coupled to the cathode of triode 245 through resistors 250 and 251 in series. The anode of triode 245 is cross-coupled to the cathode of triode 244 through resistors 252 and 253 in series. The load is taken between the common junction 25% of resistors 250 and 251 and the common junction 255 of the resistors 252. and 253. The output is fed from junctions 254 and 255 through resistors 256 and 257 to the signal input terminals 163a of a balanced amplifier and modulator generally indicated at 168. The amplifier and modulator 163 may be of any suitable conventional construe tion and has AC. power input terminals 16% connected to a suitable source of A.-C. power and AG. power output terminals 1680 connected to the primary winding 253 of a transformer 259'. The transformer 259 has a secondary winding 26%} connected in a simple series circuit with one winding 172a of the X motor 172.

The potential across the secondary winding 26% is sampled by the sampler 173 at the peaks of the waves,

and the sampled potential is stored on the capacitor 177'. The sampler 173 comprises two triodes 261 and 262. The controlelectrode of tr-iodes 261 is connected .to the cathode through a resistor 263 and; also through a capacitor 264 in series with a secondary winding 265, the series group being in parallel with the resistor 263. The primary winding 266 associated with the secondary Winding 264 is connected to the same A.C. source which supplies power to the amplifier 168. The grid circuit of triode 262 is similar to that of triode 261 and includes a resistor 2-67, a capacitor 268, a secondary winding 269 and a primary winding 276?, connected tothe same AC. source.

The triodes 261 and 262 draw grid current sufficient to. establish biasing potentials on the capacitors 264 and 258 to keep the triodes cut off except at the peaks of the applied potential. The conduction at the peaks is sufficient to maintain the charges on the biasing capacitors. 2.63. and 268 and also to supply the peak voltages to the capacitor 177. Capacitor 177 is connected in .series with capacitor 163 between the control grid 245g :of triode 245 and ground. This connection is easily seen inFIG. 5, and may :be traced in FIG. 8 from grid 245g through a wire .271, capacitor 177, Wires 272, 273, 274 and 275, and thence through capacitor 163 to ground.

The comparator 164 supplies :to the amplifier 168 a signal :of sufficient magnitude to maintain the feedback signal at grid 245g substantially equal to the input signal at grid 244g. The feedback signal is in part supplied by .the capacitor 163, so that the only part of the feedback signal effective to control the motor 172 is that part supplied by capacitor 177. As explained above, the potential on capacitor 163 is the datum reference potential for all the channels. It is utilized simply to transmit the variations in the control potentials accurately and itself has no proper function in the control of the motor 172. It is balanced out in the comparator 164so that the outv.put of that comparator which controls the current flow .through winding 172a is only that portion of the input signal which is not due to the datum potential.

The details of the amplifier circuits such as that shown diagrammatically at 168 may be the same as that shown and described completely in my copending application filed concurrently herewith and mentioned above.

In a similar manner, the sampler 159 drives the comparator and through it the amplifier 169 which sup- .plies current to the winding 17211 of motor 173.

In this fashion, a shaft driven by the motor 172 may be made to repeat the angular position and direction of rotation of the shaft '1 which controls the signals recorded on tracks 3 and 4 of themagnetic record medium. Similarly, the motor 181 may be made to repeat the changes in angular position of the shaft 2 which changes were recorded on the tracks 7 and 8 of the record medium. If the record medium was driven at the same speed during the recording and reproducing operations, then speeds of th shafts driven by the motors 172 and 181 will be the same as the speeds of the shafts 1 and 2. However, even though the record medium is driven at a different speed during reproducing than it was during recording, the relative speeds of the two shafts driven by the motors 172 and 181 will be the same as the relative speeds of the shafts 1 and 2. The motors 172 and 181 are used to drive coordinately related shafts of a tracer mechanism. Consequently, the patterns traced by the tracer mechanism will be the same regardless of the speed of operation of the record track during reproduction. If the tracer mechanism is used to drive a cutting device such as that illustrated and described in my copending application filed concurrently herewith and entitled Line Tracer Apparatus and Method, as described above, then the size of the pieces. cut by the cutter head will depend upon the speed at which the record medium is driven past the reproducing head. It is therefore possible to produce work pieces of varying sizes but of the same shape from a single pattern. It is also possible to draw the pattern to scale on a relatively small sheet of paper and have the tracer controlled cutting mechanism produce full size work pieces by following the reduced scale pattern.

While I have shown and described the preferred em bodiment of my invention, other modifications thereof will readily occur to those skilled in the art, and I therefore intend my invention to be limited only by the appendedclaims.

I claim:

1. Apparatus for recording the variations in amplitude of a potential variable withina limited range, comprising means. for producing electrical cycle reference pulses at equally timed intervals; a magnetic record medium having three record tracks, means for recording magnetic bits corresponding to said cycle reference pulses on one of the tracks, means for producing electrical datum reference pulses at fixed intervals between the cycle reference pulses, means for recording magnetic bits corresponding to said datum reference pulses on another of said tracks, means for establishing a datum potential within said limited range and corresponding to the timing of the datum pulses within the intervals limited by the cycle reference pulses, means for sampling said variable potential at a fixed time during each cycle, means responsive to said sampling means for producing, during each cycle, an information pulse displaced in time from the datum pulse in that cycle by an interval varying in accordance with the difference between the sampled potential and the datum potential, and means for recording magnetic bits corresponding to the information pulses on the third track of the record medium.

2. Apparatus for recording variation in a plurality of variable conditions, comprising means for varying a cor responding plurality of electrical potentials over a limited range as functions of the variable conditions, means for producing electrical cycle reference pulse at equally timed intervals, a magnetic record medium having a plurality of tracks equal in number to the number of conditions to be recorded plus two, means for recording ma netic bits corresponding to said cycle reference pulses on one of the tracks, means for producing electrical datum reference pulses at fixed intervals between the cycle reference pulses, means for recording magnetic bits corre sponding to said datum reference pulses on another of said tracks, means for establishing a datum potential within said limited range and corresponding to the timing of the datum pulses within the intervals limited by the cycle reference pulses, means for sampling each of said varying potentials at a fixed time during each cycle, means responsive to said sampling means for producing, during each cycle and for each potential, an information pulse displaced in time from the datum pulse in that cycle by an interval varying in accordance with the difference between the sampled potential and the datum potential, and means for recording magnetic bits corresponding to the respective information pulses on respective separate tracks of the record medium.

3. Apparatus for coding variations in amplitude of a potential variable Within a limited range, comprising means for cyclically producing elecrtical datum reference pulses at fixed intervals, means for establishing a datum potential within said limited range and corresponding to the timing of the datum pulses, means for sampling said variable potential at a fixed time during each cycle, means responsive to said sampling means for producing, during each cycle, an information pulse displaced in time from the datum pulse in that cycle by an interval varying in accordance with the diiference between the sampled potential and the datum potential, said information pulse producing means comprising a phantastron circuit, including a pento-de; said sampling means comprising means for applying the variable potential to the anode of the phantastron pentode, and means for applying to the control grid of the phantastron pentode a negative-going pulse at a time during each cycle fixed with respect to the datum pulse, said phantastron circuit being effective to produce an output pulse at a time thereafter dependent upon the amplitude of the anode potential at the instant the pulse was received at the control grid.

4. Apparatus as defined in claim 3, in which said pulse applying means comprises a triode having an anode, a cathode and a control electrode, a capacitor coupling the cathode of the triode to the pentode control grid, means directly connecting the control electrode to the pentode anode, and means coupling the negative-going pulse to the pentode anode.

5. Apparatus for reproducing a variable potential, comprising a magnetic record of said potential including three parallel record tracks on a magnetic record medium, a first of the tracks having recorded thereon equally spaced cycle reference pulses, a second of the tracks having recorded thereon equally spaced datum reference pulses at times fixed within each cycle and calibrated to represent a fixed potential value, the third track having recorded thereon information pulses, each spaced from the datum pulse of its associated cycle by a time interval--- varying from one cycle to the next as a function of said variable potential, cycle reference pulse pickup means, a saw-tooth wave generator triggered by said cycle reference pulse pickup means, datum reference pulse pickup means, first sampler means triggered by the datum reference pulse pickup means for sampling the saw-tooth wave, means for storing between cycles the potentials determined by the sampler means, information pulse pickup means, second sampler means triggered by the information pulse pickup means, and second means for storing between cycles the potentials determined by the second sampler means.

6. Apparatus for reproducing a. pattern outline, comprising tracer means including two coordinately related rotatable shafts, a split phase motor for driving each shaft, a magnetic record of the pattern outline including six parallel record tracks on a magnetic medium, a first of the tracks having recorded thereon equally spaced cycle reference pulses, a second of the tracks having recorded thereon equally spaced datum reference pulses at times fixed within each cycle and calibrated to represent a fixed potential value, each of the other four tracks having recorded thereon information pulses, each spaced from the datum pulse of its associated cycle by a time interval varying from one cycle to the next as a function of one of four variable potentials, respective pairs of said four potentials representing two-phase energizing po tentials for respective ones of said motors, cycle reference pulse pickup means, a saw-tooth wave generator triggered by said cycle reference pulse pickup means, datum reference pulse pickup means, first sampler means triggered by the datum reference pulse pickup means for sampling the saw-tooth wave, means for storing between cycles the potentials determined by the sampler means, information pulse pickup means, comprising a pickup unit for each information track, four information samplers, one for each information track, each triggered by the information pulses on its associated track, and means including said samplers for controlling said motors to reproduce said outline.

7. Apparatus for reproducing a pattern outline as defined in claim 6, including means for maintaining the say -tooth amplitude substantially constant over a 10 to 1 range of playback speeds, so that the pattern outline reproduced is unaffected by the playback speed.

8. Apparatus for translating and reproducing a variable amplitude signal without attenuation comprising a transmitting apparatus, receiving apparatus, a multiple channel transmission link connecting said transmitting and receiving apparatus, and subject to attenuation of variable amplitude signals; said transmitting apparatus comprising means for producing a first reference series of discrete electrical pulses, equally separated in time and defining successive transmission cycles, said pulses occurring at a frequency substantially higher than the highest frequency component of said variable potential, means for producing a second datum series of discrete electrical pulses, equally separated in time and separated by fixed intervals from the reference pulses, means for establishing a datum relationship between said fixed intervals and a particular value of potential, mean for sampling said variable potential concurrently with each of said reference pulses and producing a tm'rd information series of discrete electrical pulses, separated in time from the datum pulses by intervals varying as a function of the sampled values of said variable potential, and means for transmitting said first, second and third series of pulses respectively to first, second and third channels of the transmission link; said receiving apparatus comprising means responsive to said first series of pulses to generate an electrical potential having a sawtooth wave form with peaks synchronized with the pulses of said first series, first means for sampling said sawtooth potential at times concurrent with said second series of pulses, first means for storing the values of potential determined by said first sampling means, second means for sampling said sawtooth potential at times concurrent with said third series of pulses, second means for storing the values of potential determined by said second sampling means, and means for adding said stored values algebraically to reproduce the variable potential.

9. Translating and reproducing apparatus as defined in claim 8, in which said means for establishing a datum relationship includes a coincidence circuit having two inputs and an output, means connecting one input to said datum pulse producing means, and means for adjusting the potential at the other input to the value which just causes pulses at the output concurrently with said datum pulses.

10. Translating and reproducing apparatus as defined in claim 8, in which said sampling means comprises a phantastron circuit including a pentode having an anode supplied by said variable potential and a control electrode connected to said means for producing reference pulses, said phantastron circuit being tripped by the reference pulses and producing an output pulse delayed after each tripping by a time proportioned to the anode potential at the instant of tripping.

11. Translating and reproducing apparatus as defined in claim 10, in which said phantastron circuit has a maximum time delay shorter than the interval between two reference pulses.

12. Translating and reproducing apparatus as. defined in claim 8, in which said sawtooth generating means comprises timing means responsive to each reference pulse to establish a time delay interval between each reference pulse and the beginning of each sawtooth wave, and the sawtooth potential has a duration shorter than the difference between the period separating two reference pulses and the time delay interval.

13. Apparatus for positioning a rotatable shaft, comprising a magnetic record of two variable potentials cooperating to determine the shaft position, said record including three parallel record tracks on a magnetic record medium, one of said tracks having recorded thereon equally spaced reference pulses, two of said tracks having recorded thereon information pulses, one on each of said two tracks, for each reference pulse, each said information pulse being spaced from its associated reference pulse by a distance varying as a function of one of said variable potentials, pickup mean for said reference pulses, a sawtooth wave generator synchronized with the pulses from said pickup means, two pickup means for the information pulses on said two tracks, and two samplers for the sawtooth wave triggered by pulses from the respective information pulse pickup means, tWo storing means for the potentials determined by the respective samplers, a two phase motor driving the shaft to be positioned, and amplifier means for energizing said motor and controlled by the potentials stored in the two storing means.

References Cited in the file of this patent UNITED STATES PATENTS 2,531,642 Potter Nov. 28, 1950 2,531,850 Kerkhof Nov. 28, 1950 2,589,465 Weiner Mar. 18, 1952 2,656,524 Gridley et al. Oct. 20, 1953 2,679,037 OKeefe May 18, 1954 2,698,410 Madsen et al -2 Dec. 28, 1954 2,714,202 Downing July 26, 1955 2,765,459 Winter Oct. 2, 1956 2,791,640 Wolfe May 7, 1957 2,797,316 Reinhard June 25, 1957 2,822,531 Carroll Feb. 4, 1958 2,858,427 Luther Oct. 28, 1958 2,872,572 Burrows Feb. 3, 1959 2,883,650 Brockway Apr. 21, 1959 2,900,443 Camras Aug. 18, 1959 

1. APPARATUS FOR RECORDING THE VARIATIONS IN AMPLITUDE OF A POTENTIAL VARIABLE WITHIN A LIMITED RANGE, COMPRISING MEANS FOR PRODUCING ELECTRICAL CYCLE REFERENCE PULSES AT EQUALLY TIMED INTERVALS, A MAGNETIC RECORD MEDIUM HAVING THREE RECORD TRACKS, MEANS FOR RECORDING MAGNETIC BITS CORRESPONDING TO SAID CYCLE REFERENCE PULSES ON ONE OF THE TRACKS, MEANS FOR PRODUCING ELECTRICAL DATUM REFERENCE PULSES AT FIXED INTERVALS BETWEEN THE CYCLE REFERENCE PULSES, MEANS FOR RECORDING MAGNETIC BITS CORRESPONDING TO SAID DATUM REFERENCE PULSES ON ANOTHER OF SAID TRACKS, MEANS FOR ESTABLISHING A DATUM POTENTIAL WITHIN SAID LIMITED RANGE AND CORRESPONDING TO THE TIMING OF THE DATUM PULSES WITHIN THE INTERVALS LIMITED BY THE CYCLE REFERENCE PULSES, MEANS FOR SAMPLING SAID VARIABLE POTENTIAL AT A FIXED TIME DURING EACH CYCLE, MEANS RESPONSIVE TO SAID SAMPLING MEANS FOR PRODUCING, DURING EACH CYCLE, AN INFORMATION PULSE DISPLACED IN TIME FROM THE DATUM PULSE IN THAT CYCLE BY AN INTERVAL VARYING IN ACCORDANCE WITH THE DIFFERENCE BETWEEN THE SAMPLED POTENTIAL AND THE DATUM POTENTIAL, AND MEANS FOR RECORDING MAGNETIC BITS CORRESPONDING TO THE INFORMATION PULSES ON THE THIRD TRACK OF THE RECORD MEDIUM. 